The invention relates generally to magnets.
More particularly, the invention relates to composite magnets and to devices with floating magnetic bearings.
Magnets made of iron, neodymium, Sm2Co17, etc. are known. They are mostly in the form of a rod, a needle or a horseshoe. In these magnets, the two ends contain the north pole and the south pole, respectively. The magnetic field lines flow from pole to pole, and some of these field lines extend outwards of the magnet. The curved shape of the magnetic field lines is known and can be easily depicted by spreading steel chips on a piece of paper or by appropriate measuring instruments. These phenomena indicate that a conventional magnet is unable to provide a magnetic field having a unipolar region, i.e., the north pole is always significantly influenced by the south pole and vice versa.
The British patent specification 935,215 discloses pyramidal magnets whose height equals one-half the length of the base. The tips of the pyramids contain one pole and the bases contain the other pole. Six identical pyramids are combined to form a cube whose surface is presumed to have only the polarity of the bases of the individual pyramids. The opposite pole is presumed to be in the center of the cube. Based on the recognition that the field lines of a magnet run from the north pole to the south pole externally of the magnet, it follows that the surface of a cube according to the British patent specification is not unipolar. Instead, if it is even possible to assemble the pyramids, the surface of the resulting cube has north and south poles. Precise measurements with the most modern measuring instruments have confirmed this. Accordingly, unipolarity cannot be achieved with these teachings.
U.S. Pat. No. 4,222,021 discloses a magnet which, in principle, is assembled in the same manner from a set of individual magnetic bodies. A difference is that the center of the magnet of the U.S. patent has a cavity whose surface is presumed to be magnetized oppositely to the outer surface of the magnet. As indicated by measurements, the magnet obtained upon assembly of the individual magnetic bodies again has an outer surface with a north pole and a south pole or with several regions which are partially north and partially south. Moreover, the strength of such composite magnets is substantially less than that of the individual magnetic bodies constituting the same. A unipolar outer surface cannot be achieved with a magnet constructed according to this U.S. patent.
Also known are magnets in which one of the two poles, as well as the portion of the magnet between the poles, is surrounded by a jacket. The magnetic field of the covered pole is thus shielded and the normal curvature of the field lines from pole to pole is sharply reduced. The field lines run almost exclusively inside the pot-shaped shield, and a short circuit of the field lines occurs therein. Such magnets are used in electronic instruments, e.g., monitors. The shield is intended to prevent the magnets from interfering with surrounding electronic elements.
Further known are bearing arrangements employing permanent magnets. For example, the German patent 2,951,010 describes a permanent magnet radial bearing for high-speed gas centrifuges. The bearing consists of two coaxial, permanent magnet rings which are arranged one inside the other and which, due to their identical magnetization in the preferred axial direction, repel one another. Such radial bearings are suitable for high-speed rotary centrifuges where the mass to be supported by the bearing is small. A transfer of this known bearing technology to larger machines is limited by the current limitations in the production of hollow, cylindrical magnets.
Another magnetic bearing is taught in the U.S. Pat. No. 4,186,567. Here, a rotary component is radially supported on a stationary component by magnetic rings on the two components. The rings are magnetized axially and are disposed one above the other in such a manner that the direction of magnetization alternates. A permanent magnet and a diamagnetic body are arranged next to one another in the axial direction to stabilize the rotary component. This extra diamagnetic body required for axial stabilization is composed of a superconducting material and may, for instance, be in the form of a superconducting coil having a current density of approximately 105 amperes per square centimeter.
The Japanese publication 55-60719 discloses a bearing arrangement in which both the axial and the radial forces for a bearing are produced by permanent magnets. A shaft is mounted in a bearing housing and radial support is achieved by magnetic rings on the shaft and corresponding magnetic rings on the housing. As explained previously, the field lines running from the north pole to the south pole of superimposed magnets influence the magnetic field at the surface. Hence, the arrangement known from the Japanese publication is unable to create a surface having an optimun unipolarity with reference to the surface of an oppositely disposed component.